The present invention relates to a method and display device for measuring and displaying the quantity of water dampening the face of an offset printing plate.
The quantity of water dampening the face of an offset printing plate must be controlled with a high degree of accuracy. So far whether or not the face of an offset printing plate is sufficiently dampened with water is visually detected by an operator who detects the light beam reflected from the layer of water over the face of the plate or who detects visually a printed pattern.
However, when the quantity of water dampening the face of a printing plate is visually observed and controlled by an operator, the results are different from one operator to another. Furthermore, reproducibility is very low. As a result, the quantity of dampening water cannot be controlled.
Therefore there has been a strong demand for a method for measuring the quantity of water dampening the face of an offset printing plate without the visual inspection by an operator and there have been devised and demonstrated various methods utilizing the measurement of the quantity of light beam reflected from the surface of water on the face of the printing plate or the measurement of the quantity of the infrared rays absorbed.
However, when these methods are used in practice, detecting means must be disposed adjacent to the plate cylinder of a press. As a result, the space for installation of such detecting means is limited and the detecting means are contaminated by ink mist. Therefore the above-described methods are not satisfactory in practice in view of environmental conditions, working conditions, sizes, universality and cost.
Especially the environmental conditions have adverse effects. For instance, a light sensor is exposed to normally airborne dust and ink mist scattered from an inking roller so that the output of the light sensor drops to half within about two weeks. Therefore it is important that the device for measuring the quantity of dampening water be able to protect the light sensors from being contaminated and be able to calibrate the gain of the light sensors.